Via Slate, a polemic I wish I'd written: Two spaces after a period: Why you should never, ever do it. And of all people, Julian Assange stands indicted of this error. Excerpt:
Here's a fellow who's been using computers since at least the mid-1980s, a guy whose globetrotting tech-wizardry has come to symbolize all that's revolutionary about the digital age. Yet when he sits down to type, Julian Assange reverts to an antiquated habit that would not have been out of place in the secretarial pools of the 1950s: He uses two spaces after every period.
Which—for the record—is totally, completely, utterly, and inarguably wrong.
Oh, Assange is by no means alone. Two-spacers are everywhere, their ugly error crossing every social boundary of class, education, and taste.
You'd expect, for instance, that anyone savvy enough to read Slate would know the proper rules of typing, but you'd be wrong; every third e-mail I get from readers includes the two-space error. (In editing letters for "Dear Farhad," my occasional tech-advice column, I've removed enough extra spaces to fill my forthcoming volume of melancholy epic poetry, The Emptiness Within.)
The public relations profession is similarly ignorant; I've received press releases and correspondence from the biggest companies in the world that are riddled with extra spaces. Some of my best friends are irredeemable two spacers, too, and even my wife has been known to use an unnecessary extra space every now and then (though she points out that she does so only when writing to other two-spacers, just to make them happy).
What galls me about two-spacers isn't just their numbers. It's their certainty that they're right. Over Thanksgiving dinner last year, I asked people what they considered to be the "correct" number of spaces between sentences. The diners included doctors, computer programmers, and other highly accomplished professionals. Everyone—everyone!—said it was proper to use two spaces.
Some people admitted to slipping sometimes and using a single space—but when writing something formal, they were always careful to use two. Others explained they mostly used a single space but felt guilty for violating the two-space "rule." Still others said they used two spaces all the time, and they were thrilled to be so proper.
When I pointed out that they were doing it wrong—that, in fact, the correct way to end a sentence is with a period followed by a single, proud, beautiful space—the table balked. "Who says two spaces is wrong?" they wanted to know.
Typographers, that's who.